1. Field of the Invention
The present invention relates to a regularly-shaped aluminosilicate. More specifically, the invention relates to a regularly-shaped aluminosilicate exhibiting excellent pigment property, being capable of being easily dispersed in a resin, enabling the blending operation to be favorably carried out, and useful as a blending agent for resins or for coating materials.
2. Prior Art
As a filler for various polymer films, resins or rubbers, it has been desired to develop an inorganic filler having a predetermined particle shape and which undergoes little secondary aggregation.
It has been known that zeolite has a predetermined particle shape and imparts antiblocking action when it is blended in a resin. According to, for example, Japanese Patent Publication No. 16134/1977, the anti-blocking property of a biaxially drawn film is improved by adding a zeolite powder having an average particle diameter of not larger than 20 microns in an amount of 0.01 to 5% by weight to a polypropylene.
Furthermore, Japanese Patent Publication No. 36866/1986 discloses an alumina-silica resin blending agent comprising primary cubic particles having a side of not longer than 5 microns and having an Al.sub.2 O.sub.3 :SiO.sub.2 molar ratio of from 1:1.8 to 1:5, being substantially amorphous from the viewpoint of X-ray diffraction and having a BET specific surface area of not larger than 100 m.sup.2 /g.
Nepheline syenite which is a natural silicate is a mineral produced in Canada, and the powder obtained by finely pulverizing and classifying this mineral has been placed on the market under the trade name "Minex", and has been blended in resins (Japanese Laid-Open Patent Publication No. 234984/1990).
However, zeolite adsorbs the water (called zeolitic water). When a resin is blended with zeolite and is heated, therefore, the above-mentioned water is released giving rise to the occurrence of foaming. It has therefore been desired to provide an aluminosilicate blending agent which is inert and exhibits little adsorptive property.
The above-mentioned amorphous aluminosilicate resin blending agent comprises particles of a predetermined shape without containing base component of zeolite, causes the molded resin articles to be little colored, and exhibits small surface activity and adsorption compared to zeolite but yet exhibits hygroscopic property. When the blending agent after being left to stand under highly humid conditions is mixed into a resin, therefore, problems arise such as foaming, etc.
Furthermore, the product obtained by pulverizing and classifying the nepheline syenite, which is a naturally produced aluminosilicate mineral, is used as a blending agent for resins or coating materials because it exhibits a very small hygroscopic property.
However, the particles of the above product have indefinite shapes exhibiting a broad particle size distribution. Therefore, this blending agent is still not satisfactory for the purpose of accomplishing a desired anti-blocking property when blended in a relatively small amount. Moreover, the natural product contains many impurities leaving room for improvement from the standpoint of the quality of dispersion. Moreover, the particles have sharp corners specific to a mechanically pulverized product and exhibit abrasive properties.
It is therefore an object of the present invention to provide a regularly-shaped aluminosilicate having a predetermined composition and comprising regularly-shaped particles, and having a symmetrical particle size distribution, exhibiting low hygroscopic property and excellent pigment property.
Another object of the present invention is to provide a blending agent for resins or coating materials having a high pigment volume concentration, capable of being easily blended and dispersed in resins and in coating materials, and enabling the blending operation to be favorably carried out.
According to the present invention, there is provided a regularly-shaped aluminosilicate comprising cubic or spherical regularly-shaped particles having a chemical composition expressed by the following formula (1), EQU mM.sub.2/x O.multidot.Al.sub.2 O.sub.3 .multidot.nSiO.sub.2( 2)
wherein m is a number of from 0.9 to 1.1,M is at least one of Na, K, Ca, Mg or Zn, x is a valency of M, and n is a number of from 1.9 to 3.6 and, preferably, from 1.9 to 3.4, PA1 wherein D.sub.25 represents a particle diameter at 25% of a cumulative particle size distribution on the volume basis as measured by a Coulter method, and D.sub.75 represents a particle diameter at 75% thereof,
and having a nepheline type or a carnegieite crystalline structure, said regularly-shaped particles having an apparent specific gravity of from 0.3 to 0.8 g/cm.sup.3, an amount of oil absorption of not larger than 50 ml/100 g, a refractive index of from 1.46 to 1.56, and an amount of moisture absorption of not larger than 1% when the particles are exposed to an atmosphere of a relative humidity of 90% and a temperature of 20 to 25.degree. C. for 48 hours.
The above-mentioned regularly-shaped aluminosilicate:
1. Is obtained by firing a synthetic A-type zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of from 1.9 to 2.2 and particularly at a temperature of not lower than 800.degree. C.;
2. Is obtained by firing a synthetic Pc-type zeolite having an SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio of from 2 to 3.6 and, particularly, from 2 to 3.4 at a temperature of not lower than 800.degree. C.;
3. Has an average particle diameter of from 0.5 to 30 .mu.m and, preferably, from 0.5 to 25 .mu.m;
4. Has a sharpness (DP) of particle size distribution defined by the formula D.sub.75 /D.sub.25,
of from 1.2 to 2.9; and
5. Has a Mohs' hardness of not larger than 6.
According to another embodiment of the present invention, there is provided a blending agent for resins, a blending agent for coating materials and a blending agent for crystalline glasses, comprising the above-mentioned regularly-shaped aluminosilicate.